People also make the point that a kid would be better off with a gay couple than either in care or with junkie parents...however, this only deals with the effect, not the actual problem.

Said it before, introduce a baby license...
1) every male baby has a reversible sterilisation
2) When they meet someone and are old enough to be a parent, they can apply for the license.
3) criteria would be set fairly ie both are emotionally and financially secure and whatever else was reasonable
4) its reversed only after the partner is pregnant

People whine about the restrictions of human rights and how draconian it is, but if you're able to provide fairly basic financial and emotional support, what's the problem? It shouldn't be a "right" to have kids if you simply cannot provide for one.
Advantages?

1) dramatically reduce nearly every state benefit
2)mainly guarantee kids are brought up in as best an environment they can
3)slow down over population
4) improve the education system
5) reduce medical service costs and improve the overall service
6) reduce child poverty and neglect
You could go on and on and on....

Gay people could adopt kids currently in the care system without any problem. I think the historical evidence we have for the long term negative impact the care system causes to many kids outweighs whatever feelings people might have about a balanced upbringing etc

I can almost guarantee something like this will need to happen down the line.